In centrifugal apparatuses, the direction of the fluid flow is independent from the rotational direction of the centrifugal apparatus impeller. However, if the centrifugal apparatus is rotated in the wrong direction, the produced flow rate and pressure may drop dramatically compared with the correct rotational direction. This also reduces significantly the energy efficiency of the centrifugal apparatus.
The correctness of the rotational direction of a centrifugal apparatus should be checked in connection with installation of the centrifugal apparatus, and after any maintenance operation that could change the rotational direction of the centrifugal apparatus.
Traditionally, the correct rotational direction of a centrifugal apparatus is determined by visually inspecting the rotational direction. This requires additional personnel and is not an automated function. In addition, the centrifugal apparatus can be in such a position that the visual inspection is impossible to carry out.
U.S. Patent Application Publication No. 2010/0316503 discloses a pump unit which includes a rotation direction recognition module for automatic recognition of the correct rotation direction of the pump. In this publication, the value of flow rate, pressure or power is measured and compared between the reverse rotation and forward rotation cases. If there is a difference in the static state measurement signals between the forward and reverse rotational directions, the right rotational direction can be distinguished.
However, in the above-mentioned pump system, additional instrumentation might be required to be installed in to the pump system when the flow rate or pressure is used as the signal to be compared. Another drawback relates to a situation where power estimates produced by a frequency converter driving the pump are used as the signals to be compared. This drawback results from the fact that in pump systems it is not uncommon that forward and reverse rotational speeds have the same shaft power requirement. Consequently, in many cases, it is impossible to decide the correct rotational direction based on the power estimates.